Calibration of the Watermark 200SS moisture sensor for irrigation scheduling in five soil types in Zacatecas, Mexico

Resumen

Objective: To develop an irrigation scheduling methodology based on the calibration of WATERMARK 200SS sensors, aimed at optimizing water use for six key crops garlic, chili, maize, oats, alfalfa, and beans in agricultural soils of Zacatecas, Mexico, considering their hydro-physical properties and specific crop water requirements.

Design/methodology/approach: Five soil types were characterized based on bulk density, texture, organic matter content, and water retention curves using the van Genuchten model. WATERMARK sensors were calibrated through polynomial models (R² > 0.96) to correlate sensor readings (centibars, cbar) with gravimetric soil moisture content. The proposed irrigation scheduling framework integrated: (1) soil water balance, (2) critical tension thresholds (0.3–1.0 atm), and (3) real-time sensor data, tailored for drip irrigation systems operating at 95% efficiency.

Results: Clay soils (Samples 1 and 5) demonstrated greater water retention capacity (Hₛ up to 0.231 cm³/cm³), whereas sandy loam soil (Sample 2) exhibited rapid drainage (α = 0.022). Calibration curves for the sensors achieved high precision (RMSE < 0.007), ensuring accurate estimation of soil moisture within optimal agronomic thresholds, spanning from field capacity to the permanent wilting point. Irrigation depths were determined per crop, based on soil water tension data derived from the calibrated sensors.

Limitations/implications: The methodology necessitates in situ calibration for each soil type and does not address uncontrolled spatial variability. Nevertheless, it offers a practical and scalable solution for farmers in arid regions, reducing dependence on empirical irrigation methods.

Findings/conclusions: WATERMARK 200SS sensors, when calibrated using localized models, effectively enable precision irrigation scheduling. This methodology significantly improves water-use efficiency across essential crops, providing resilience against climatic stressors in the semi-arid context of Zacatecas